Re: wellcraft nova
The only thing I've seen ready on the shelf is the cockpit cover. An extensive internet search may find a shop that still has templates or something. Otherwise you may have to have one custom made.
My Nova II came with a bimini top that has the clear zip-in front and sides (didn't come with the rear). It's a Sunbrella, maybe they still carry the complete sets, or can make a set for you.